Method of producing polydiorganosiloxane gum

Abstract

During the polymerization of diorganocyclosiloxane, to produce a polymer for use in manufacturing silicone rubber, a small amount of --SiOH is formed. The amount of --SiOH present in the polymer can be controlled by controlling the water vapor pressure present in the reaction container during polymerization.

That which is claimed is: 
     
       1. A method for controlling the amount of silanol ends remaining after the polymerization of diorganocyclosiloxane in the presence of acid or base catalyst comprising, (A) polymerizing, in a sealed container having an inert gaseous sweep of controllable water vapor pressure, diorganocyclosiloxane in the presence of acid or base catalyst under conditions of controlled water vapor pressure. the dew point of the exiting gaseous sweep being less than -10° C. then   (B) terminating the polymerization process and neutralizing the catalyst before exposure to uncontrolled water vapor in the atmosphere.   
     
     
       2. The method of claim 1 in which the catalyst is a base. 
     
     
       3. The method of claim 2 in which the catalyst is potassium silanolate. 
     
     
       4. The method of claim 2 in which the catalyst is neutralized with an acid. 
     
     
       5. The method of claim 3 in which the catalyst is neutralized with dimethylvinylsilylacetate. 
     
     
       6. The method of claim 1 in which the exiting gaseous sweep has a dew point of less than -30° C.